358 Experimental Zoology 



been found that virgin eggs produce males, but von Siebold ob- 

 tained 13 females among 1700 males; he thinks these may have 

 been introduced with the food. '' Other observers have obtained 

 only males." 



In another group, the gallflies, Cynipidse, females appear 

 in preponderating numbers and reproduce by parthenogenesis 

 in one generation at least. Males in some forms are of the rar- 

 est occurrence, and have never been found in some species. 

 It has been observed, however, that in some species the eggs 

 produced by the parthenogenetic females give rise to insects, 

 both male and female, quite different in appearance from the 

 parthenogenetic generation. The complete life histories of 

 some of these species have been given on page 268 in describ- 

 ing the formation of galls. According to Adler, not more than 

 2 per cent of males appear in the sexual generation of Rhodites 

 rosae and R. eglantcnas. The female of Phromah lays her egg 

 in the caterpillar of Vanessa urticse. In several cases caterpillars 

 were reared, which were kept uncontaminated, and an unfer- 

 tihzed female of Phromah deposited eggs in them. ^ When the 

 flies emerged from the pupa there were found in one case 124 

 males, in another case 62 males, in a third case 75 males and 5 

 females, and in a fourth case 45 males and 4 females. Thus 

 while the unfertilized eggs of this species produce males, occa- 

 sionally females also appear. 



These cases serve as a warning not to insist with too much 

 positiveness on the view that in the bee unfertilized eggs always 

 produce males, since they show that exceptions to such a rule 

 may sometimes occur. 



LITERATURE, CHAPTER XXIII 



Cameron. Monograph of Phytophagus Hymenoptera. 1882-1884. 

 Casteel, D., and Phillips, E. Comparative Variability of Drones and 



Workers of the Honey Bee. Biol. Bull. VI. 1903. 

 DiCKEL, F. Das Prinzip der Geschlechtsbildung. Darmstadt. 1898. 

 Meine Ansicht iiber die Freiburger Untersuchungsergebnisse von Bien- 



eneiern. Anat. Anz. XIX. 1901. 

 Ueber Petrunkewitsch's Untersuchungsergebnisse von Bieneneiern. 

 Zool. Anz. XXV. 1901. 



